It has been a desire to provide pressure transducers which can operate at high temperatures without corroding and which are simple to construct. The prior art is replete with patents and devices which can operate at relatively high temperatures. Such devices include silicon sensors which operate for example at temperatures of 600° C. or higher. Other patents which are assigned to the assignee herein, namely Kulite Semiconductor Products, Inc., depict silicon carbide transducers which are capable of extremely high temperature operation. The prior art is replete with patents which utilize metal as deflecting diaphragms. Onto these metal diaphragms are affixed piezoresistive or other type of sensors. The diaphragms being made of metal are capable of operating at high temperatures. Sensors affixed to the diaphragm can include wire strain gauges or other types of semiconductor strain gauges. Such gauges have to be placed onto the diaphragm in specific positions and each individually affixed to the diaphragm at specific positions. Accordingly, the placement of the sensors on the diaphragm can be a time consuming task.
In the prior art, there were two principal methods of making miniature high temperature pressure transducers. In the first method, a thin metallized isolation diaphragm was mounted in front of the sensor and the pressure was transmitted to the sensor by a small volume of oil. As pressure was applied to the isolation diaphragm, pressure was transmitted to the sensor by the oil, which is a non-compressible fluid. As long as the oil retains its property as a non-compressible fluid, such a pressure transducer operates properly. However, as the temperature increases, the vapor pressure of the oil increases to a point where the oil no longer transmits the pressure to the sensor, setting an upper temperature limit on the operation of the transducer. In the second method, as individual gauges are affixed to the diaphragm, using either a high temperature cement or glass. In this method the only dielectric isolation between the gauge and the metal diaphragm is the cement itself. Any variations in the thickness of the cement can cause electrical breakdowns at relatively low temperatures, causing the transducer to fail. Furthermore, if the individual gauges are made from silicon, in order to obtain sufficient resistance, the gauge must be rather long and exhibit rather high resistivity. Thus it becomes difficult to place the individual gauge in a resistor in a region of high stress. As the temperature is increased, the relatively high resistivity material used for the sensor changes its value at a non-linear rate as the temperature is increased to a higher value, making thermal compensation very difficult. Moreover, each individual gauge must be separately applied to the diaphragm, or alternatively, if the various sensors are interconnected prior to application to the diaphragm, the structure is complex, fragile, and difficult to handle, so that the resulting transducers are of dubious quality.